1. Technical Field
The present invention relates to an optical disk drive, and more particularly to transfer control of an optical pickup.
2. Related Art
An optical disk drive has hitherto performed seeking operation by means of transferring an optical pickup in a radial direction of an optical disk by means of a stepping motor.
FIGS. 6 and 7 show the configuration of an optical disk drive and the configuration of a transfer mechanism, which are described in the related art shown in JP2003-100041A. An optical pickup 310 has a semiconductor laser (LD) and emits a laser beam modulated according to recording data, thereby recording data on an optical disk 10; and emits a laser beam of reproducing power and receives light reflected from the optical disk 10, to thus generate a reproduced signal.
A decoder 320 decodes the reproduced signal from the optical pickup 310; generates an address signal or the like; and supplies a control section 330 with the thus-generated address signal or the like.
The control section 330 comprises a CPU, ROM, RAM, and the like, and controls seeking operation. Specifically, upon receipt, from a host machine such as a personal computer or the like, of a seek operation command including a target address corresponding to a destination where the optical pickup 310 is to be transferred, the control section 330 computes the number of pulse signals to be imparted to a stepping motor 100, and supplies a controller 340 with the number of pulse signals. In accordance with the command from the control section 330, the controller 340 supplies a driver 350 with a drive control signal. In accordance with the drive control signal, the driver 350 controls the number of rotations of and the rotational speed of the stepping motor 100.
As shown in FIG. 7, the stepping motor 100 is provided with a lead screw 110 in which a helical groove is formed at a given pitch P, and the lead screw 110 is mounted in parallel with the radial direction of the optical disk 10. The optical pickup 310 is disposed so as to be movable along the groove of the lead screw 110. Every time the stepping motor 100 rotates one turn, the optical pickup 310 is moved in the radial direction of the optical disk 10 by one pitch P of the lead screw 110.
With such a configuration, the control section 330 computes a difference between the current address supplied from the decoder 320 at the end of seeking operation and the target address received from the host machine at the commencement of seeking operation. When the computed amount of positional displacement exceeds an allowable amount, the stepping motor 100 is determined to be out of step (hereinafter called a “step-out”), and the rotational speed of the stepping motor 100 is reduced. Here, the term “step-out” means a phenomenon in which the torque of the stepping motor 100 becomes deficient for reasons of an increase in a pulse frequency applied to the stepping motor 100 and in which the stepping motor 100 does not rotate even when the pulse voltage is applied to the stepping motor 100.
However, in addition to including the step-out of the stepping motor 100, the problem of the transfer mechanism also includes a problem of so-called “tooth jump” in which a teeth section 310a provided in the optical pickup 310 is disengaged from the lead screw 110. Occurrence of tooth jump leads to dissociation of a target address from a current address. The tooth jump is considered to be caused primarily by abrasion of or damage to the teeth section 310a attributable to time-varying operations, collision, or the like, or by oscillation or the like. This problem does not arise solely in the stepping motor 100 but can also arise likewise in the case of use of a DC motor.